Differential Pharmacokinetics of Diclofenac Potassium for Oral Solution vs Immediate-Release Tablets From a Randomized Trial: Effect of Fed and Fasting Conditions

ObjectiveTo compare the pharmacokinetics of, and food effect on, diclofenac potassium delivered as an oral solution vs an immediate-release tablet. BackgroundDiclofenac potassium for oral solution is the only nonsteroidal anti-inflammatory drug approved as monotherapy for the acute treatment of migraine attacks with or without aura in adults 18 years of age or older. It is formulated with potassium bicarbonate as a buffering agent to raise the pH and consequently increase the aqueous solubility of diclofenac in the acidic environment of the stomach following oral administration. The dosage is 50mg of powdered diclofenac potassium dissolved in 1 to 2 ounces (30 to 60mL) of water prior to administration, with dosing time in relation to food intake not specified - this was the case for the pivotal efficacy and safety trials in subjects with acute migraine attacks in which the primary endpoints were achieved. For acute treatment of migraine attacks, rapid onset of pain relief is desirable and is likely related to a rapid appearance of an effective concentration of the drug in the systemic circulation. The rate at which an orally administered drug reaches the blood is affected by both its formulation and the presence of food in the stomach. The present study was designed to investigate the pharmacokinetics of 2 formulations of diclofenac potassium, an immediate-release tablet and an oral solution, and to ascertain the effect of food. MethodsThis was an open-label, randomized, single-center, crossover trial in healthy volunteers. Subjects were randomized using computer-generated list to 1:1:1:1 ratio. They received a single 50-mg dose of diclofenac potassium in 4 sequences (ABCD, BADC, CDBA, and DCAB) during each of the 4 treatment periods. The 4 treatments were: A, oral solution fasting; B, tablet fasting; C, oral solution fed; and D, tablet fed. There was a 7-day washout period between dosing. Blood samples for pharmacokinetic analysis were taken for up to 12 hours post-dose and analyzed for diclofenac concentrations. Pharmacokinetic parameters, including peak concentration (C-max), time to C-max (t(max)), area under the concentration-time curve (AUC) from time 0 to last measurable concentration (AUC(t)), and extrapolation to infinity (AUC) were obtained using non-compartmental analysis. Comparative assessments for C-max and AUC were performed between the solution and tablet under fed and fasting conditions and between fed and fasting states for both formulations. Bioequivalent exposure was defined as the geometric mean ratio and its 90% confidence interval falling within 80.0-125.0% for C-max and AUC. Adverse events (AEs) were monitored throughout the trial. ResultsSixty-one percent of the 36 randomized subjects were male, 91.7% were Caucasian, and the mean (standard deviation [SD]) age was 31.9 (7.6) years. Thirty-three (91.7%) subjects completed all 4 treatments. Solution vs TabletWhen taken under fed conditions, the oral solution resulted in an approximately 80% faster median t(max) (0.17 vs 1.25 hours, P=.00015) and a 21% lower C-max (meanSD, ng/mL: 506305 vs 835449, P=.00061) compared with the tablet. AUC values were similar between the 2 formulations. When taken under fasting conditions, the oral solution exhibited a 50% faster median t(max) (0.25 vs 0.50 hours, P=.00035) to achieve a 77% higher C-max (mean +/- SD, ng/mL: 1620 +/- 538 vs 1160 +/- 452, P=.00032) compared with the tablet. AUC(t) and AUC were similar between the 2 formulations. Fed vs fastingWhen taken under fed conditions, the oral solution resulted in a similar median t(max) (0.17 vs 0.25 hours, P=.185) and 64% lower C-max (mean +/- SD, ng/mL: 506 +/- 305 vs 1620 +/- 538, P<.00001) compared with fasting conditions. In comparison, the tablets under fed conditions resulted in a statistically significantly delayed median t(max) (1.25 vs 0.50, P=.00143) and approximate to 30% lower C-max (mean +/- SD, ng/mL: 835 +/- 449 vs 1160 +/- 452, P=.00377). AUC values were similar between fed and fasting conditions for both formulations. Twelve subjects (33%) experienced 1 treatment-emergent AE during the study. All AEs were mild and resolved without treatment; none resulted in study discontinuation. More treatment-emergent AEs were reported in subjects receiving the tablet compared with the solution formulation (20.0% vs 11.8 % in fasting and 17.1% vs 8.6% in fed conditions). ConclusionsDiclofenac potassium oral solution and tablet formulations produced statistically significantly different C-max and t(max) but similar AUC under fed and fasting conditions. Fed conditions produced significantly lower C-max for both formulations and profoundly delayed t(max) for the tablet, but had no effect on t(max) for the solution formulation. These data provide insights into the importance of an earlier and greater exposure to diclofenac arising from the solution formulation than the tablet, which may account for the superiority in the onset and sustained pain reduction for the solution than the tablet formulation observed in the double-blind, efficacy/safety study in migraine patients conducted in Europe.